Noise Dose Calculator
NIOSH hearing dose percent from noise levels and hours.
What it does
Noise dose divides exposed hours by allowed hours at each level and adds them: 100% is the full daily allowance. NIOSH sets 85 dBA for 8 hours with a 3 dB exchange, so 88 allows 4 hours and 91 allows 2.
The tool above takes one or two level plus hour pairs. It returns the dose percent with the verdict and the allowed hours at the first level beside it.
The default 4 hours at 90 plus 4 at 80 totals 174.5%: over limit, since 90 allows only 2.52 hours. Eight hours at 85 alone reads exactly 100%.
The method follows NIOSH noise criteria with OSHA hearing references behind workplace limits. Both agree dose math; OSHA uses 90 dBA with a 5 dB exchange instead.
How to use
- Enter the first noise level in dBA.
- Enter the hours spent in it.
- Add a second pair or leave 0 and 0.
- Read dose first against 100%.
- Protect or shorten time when over.
Formula
- 85 / 8
- NIOSH baseline dBA with hours.
- 3 dB
- Exchange halving time per rise.
- 100%
- Full daily allowance line.
Second pair both zero means single exposure. Levels below 60 or above 140 are rejected as out of scope for this page.
Worked example
Example: 4 h at 90 plus 4 h at 80
Defaults: 90 dBA 4 h, 80 dBA 4 h.
- Allowed at 90: 8 / 2^(5/3) = 8 / 3.175 = 2.52 h.
- Share: 4 / 2.52 = 1.587.
- Allowed at 80: 8 / 2^(-5/3) = 25.40 h. Share 4/25.40 = 0.157.
- Dose: 100 x (1.587 + 0.157) = 174.5%: over.
- Tool shows 174.5%, Over limit, 2.52 h at 90 dBA.
Reference table
| Level | Allowed | Rule |
|---|---|---|
| 82 dBA | 16 h | Half intensity |
| 85 dBA | 8 h | Baseline |
| 88 dBA | 4 h | Halved |
| 91 dBA | 2 h | Quartered |
| 100 dBA | 15 min | Minutes only |
Limits
- NIOSH criteria; OSHA uses different numbers.
- Averages hide peak impulse damage.
- Protector fit decides real attenuation.
- Medical advice needs professionals.
Common mistakes
- Averaging decibels arithmetically.
- Using OSHA 5 dB math in NIOSH columns.
- Ignoring the second quieter exposure.
- Trusting foam plugs without fit checks.
- Reading 100% as safe rather than max.
Try it yourself
Quick checks. Answers sit tucked under each question.
85 dBA for 8 h?
8 / 8 = 100%: within limit exactly.
88 dBA allowed?
8 / 2 = 4 hours.
91 dBA for 1 h?
1 / 2 = 50% dose.
Questions
What is noise dose?
Exposed over allowed hours times 100: 174.5% here means over.
Why halve per 3 dB?
Decibels compress energy logarithmically; NIOSH exchange sets the slope.
NIOSH vs OSHA?
NIOSH: 85 dBA, 3 dB exchange. OSHA: 90 dBA, 5 dB exchange.
Are plugs enough?
Only fitted and worn the whole exposure; derate labeled values.
What about peaks?
Impulse bangs damage beyond averages; this page averages.
Is 100% safe?
It is the maximum, not a target. Lower always hears better.